Santorum has been laying the groundwork for months. While the two-term senator lacks the name recognition and fundraising organization of his better-known rivals, he is a favorite among the social conservatives who hold huge sway in some early nominating contests.

“Now, the only test for me is whether we can raise the money that’s necessary,” Santorum told Fox News Channel, where he worked as a contributor until the network put him on leave while he decided whether to enter the race. “We’re going to determine over the next few weeks as to whether the resources are going to be there.”

Santorum, a blunt-talking conservative who once was the No. 3 Senate Republican, has made frequent visits to early-voting states New Hampshire, Iowa and South Carolina. On Thursday, he planned a town hall-style meeting on the economy at New England College in Henniker, N.H.

“It’s time for America to be America again — an America that rewards innovation and hard work, that stands by our allies instead of our enemies, that protects even the most vulnerable of our society, and an America that says every life is to be cherished,” Santorum told supporters in an email that was sent as he announced his plans on Fox News Channel. “That’s what I believe in and that’s why I’m taking this next step in a possible run for president.”

His policy positions align with conservatives who are looking at many of the expected candidates with hesitation.

Former Massachusetts Gov. Mitt Romney‘s changes of heart on gay rights and abortion do little to help his second presidential effort. Former House Speaker Newt Gingrich is twice divorced. Former Mississippi Gov. Haley Barbour, making his first trip of the year to meet with New Hampshire voters on Thursday, has a record as a lobbyist.

Santorum, 52, also enters the campaign with hurdles to overcome. He lost his Senate seat to Democrat Bob Casey in 2006 and has been out of elective office since 2007. He lacks the robust fundraising or personal wealth of his likely rivals.

Santorum was already looking at the White House when he lost five years ago. His opposition to abortion, gay marriage and embryonic stem cell research makes him an appealing candidate for conservatives. But his sometimes abrasive style alienated voters in Democratic-leaning Pennsylvania, and they replaced him with Casey, an anti-abortion Democrat.